The present invention relates to an electric power steering apparatus, which applies power of an electric motor directly to a steering system so as to ease steering effort of the driver.
Electric power steering apparatus assists steering effort of the driver by way of applying an assist torque that is generated by directly utilizing a driving force of an electric motor to a steering system. To this end, the electric power steering apparatus is furnished with a motor control section for setting a target current supplied to the electric motor as well as for applying the target current to the electric motor with feed back control. In the motor control section, the target current is set at least on the basis of vehicle speed detected by the vehicle speed sensor. The target current is set to a higher value in the case of a lower vehicle speed having a greater road reaction force, and is set to a lower value in the case of a higher vehicle speed to secure the stability during driving. For this reason, when the vehicle speed sensor malfunctions, the vehicle speed sensor always detects the vehicle speed of 0 km/h and the motor control section sets the target current to a greater value, so that a large assist torque continues to act on the steering system. Various methods for determining failure of the vehicle speed sensor have been proposed in order to avoid applying a greater assist torque at the time of failure of the vehicle speed sensor.
The methods for determining failure of the vehicle speed sensor are given below. In a first failure determination method, two vehicle speed sensors are employed and each sensor detects the vehicle speed, so that failure of the vehicle speed sensor is detected based on the comparison between the two vehicle speeds detected. In a second failure determination method, the vehicle speed detected by the vehicle speed sensor and the engine rotational speed detected by the engine rotational speed sensor are compared to each other so as to determine failure of the vehicle speed sensor. Japanese Laid-open Patent Publication Hei.3-114974 discloses a method for determining failure of the vehicle speed sensor in a four-wheel steering apparatus. According to a third failure determination method in this four-wheel steering apparatus, the vehicle speed sensor is determined as failure in the case that the vehicle speed detected by the vehicle speed sensor is 0 km/h, that the output of the engine is capable of moving the vehicle (in the preferred embodiment, it is determined by the engine rotational speed to be detected by the engine rotational speed detecting means), and that the shift range detected by the driving range detecting means is in a driving range.
However, the first failure determination method requires two vehicle sensors, which leads to increased cost. In the second failure determination method, if the driver races (viz. idly blows) the engine while the vehicle is parked, the vehicle speed is 0 km/h notwithstanding that the engine rotational speed is equal to or greater than a predetermined rotational speed (rpm) and therefore the vehicle speed sensor is determined as failure. Especially in the case of a hybrid vehicle provided with an engine and an electric motor, because racing frequency becomes higher to charge the onboard battery, a determination error occurs frequently. In the third failure determination method, failure is determined only when the shift range is set in a driving range, and therefore, the vehicle speed sensor cannot be determined as failure when the driver races the engine while the vehicle is parked (with the shift range set in a non-driving range). However, in this third failure determination method, a determination error may arise to determine failure of the vehicle sensor at the time of abrupt starting because the shift range is set in a driving range and the engine rotational speed may be equal to or greater than a predetermined rotational speed notwithstanding that the actual vehicle speed is 0 km/h or substantially 0 km/h (the vehicle speed sensor detects the vehicle speed as 0 km/h). Moreover, in the third failure determination method, if the driving range detecting means malfunctions, it is impossible to determine failure of the vehicle speed sensor because the driving range detecting means is always off and indicates that the shift range is set in a non-driving range.
Accordingly, it is an object of the present invention to provide an electric power steering apparatus which is capable of highly accurately determining failure of the vehicle speed sensor without errors.
According to a first aspect of the present invention, there is provided an electric power steering apparatus comprising:
an electric motor applying an assist torque to a steering system;
a vehicle speed detecting section detecting a vehicle speed of the vehicle;
a shifting state detecting section detecting a shifting state of the vehicle;
an engine rotational speed detecting section detecting an engine rotational speed; and
a motor control section for controlling drive of the electric motor based on an output from the vehicle speed detecting section, wherein the motor control section includes a failure determination section for determining failure of the vehicle speed detecting section on the basis of the vehicle speed detected by the vehicle speed detecting section, the shifting state detected by the shifting state detecting section, and the engine rotational speed detected by the engine rotational speed detecting section, and wherein the failure determination section determines that the vehicle speed detecting section malfunctions if the engine rotational speed is equal to or greater than a predetermined rotational speed for a determinative continuous-time and/or a first determinative integrated time while the vehicle speed is zero and the shifting state is a vehicle driving state.
With such a constitution of the electric power steering apparatus, the failure determination section determines that the vehicle speed detecting section malfunctions, if the vehicle speed detecting section detects the vehicle speed of zero on condition that while the shifting state is a vehicle driving state, the engine rotational speed is equal to or greater than the predetermined rotational speed wherein the expected vehicle speed is greater than zero (viz. the actual vehicle speed of the vehicle would no be zero), and if such a condition continues for the determinative continuous-time and/or the first determinative integrated time. By this determination, it is possible to eliminate a determination error such that the vehicle speed detecting section is determined falsely as failure, even in the case of abrupt starting. This is because the determination conditions consider the determinative continuous-time and/or the first determinative integrated time as sufficiently long time for which the vehicle speed detected by the vehicle speed detecting section after abrupt starting would be greater than zero.
In this electric power steering apparatus, since the determination of failure of the vehicle speed detecting section concerns the vehicle speed, the engine rotational speed and the shifting state as determination factors, and further concerns the determinative continuous-time and/or the first determinative integrated time as determination conditions, it is possible to eliminate a determination error even in the case of abrupt starting. Therefore, the electric power steering apparatus ensures highly accurate determination of failure of the vehicle speed detecting section.
According to a second aspect of the present invention, there is provided an electric power steering apparatus comprising:
an electric motor applying an assist torque to a steering system;
a vehicle speed detecting section detecting a vehicle speed of the vehicle;
a shifting state detecting section detecting a shifting state of the vehicle;
an engine rotational speed detecting section detecting an engine rotational speed; and
a motor control section for controlling drive of the electric motor based on an output from the vehicle speed detecting section, wherein the motor control section includes a failure determination section for determining failure of the vehicle speed detecting section on the basis of the vehicle speed detected by the vehicle speed detecting section, the shifting state detected by the shifting state detecting section, and the engine rotational speed detected by the engine rotational speed detecting section, and wherein the failure determination section determines that the vehicle speed detecting section malfunctions if the engine rotational speed is equal to or greater than a predetermined rotational speed for a second determinative integrated time while the vehicle speed is zero and the shifting state is not a vehicle driving state.
With such a constitution of the electric power steering apparatus, the failure determination section determines that the vehicle speed detecting section malfunctions, if the engine rotational speed is equal to or greater than the predetermined rotational speed wherein the expected vehicle speed is greater than zero (viz. the vehicle would be actually moving), and if such a condition continues for the second determinative integrated time while the shifting state detected by the shifting state detecting section is not a vehicle driving state and the vehicle speed detecting section detects the vehicles speed of zero. By this determination, failure of the vehicle speed detecting section will be determined even if the shifting state detecting section malfunctions. Furthermore, even if the driver races the engine, it is possible to eliminate a determination error such that the vehicle speed detecting section is determined falsely as failure. This is because the determination condition considers the second determinative integrated time wherein the driver usually would not race the engine for such a long time.
In this electric power steering apparatus, since the determination of failure of the vehicle speed detecting section concerns the vehicle speed, the engine rotational speed and the shifting state as determination factors, and further concerns the second determinative integrated time as a determination condition, it is possible to determine failure of the vehicle speed detecting section even if the shifting state detecting section malfunctions, and further it is possible to eliminate a determination error even if the driver races the engine. Therefore, the electric power steering apparatus ensures highly accurate determination of failure of the vehicle speed detecting section.
In the aforementioned electric power steering apparatus, the shifting state detecting section may be incorporated in an engine control section, and the engine control section inputs a shifting state signal to the motor control section.
With such a constitution of the electric power steering apparatus, the shifting state detecting section is provided in the engine control section into which a signal of the shifting state is inputted, and the shifting state is determined by the shifting state signal from the engine control section. Accordingly, the electric power steering apparatus determines the shifting state with a simple constitution.
In this electric power steering apparatus, since the shifting state detecting section is incorporated in the engine control section, it is possible to simplify the construction and to thereby reduce the cost.
According to a third aspect of the present invention, there is provided an electric power steering apparatus comprising:
an electric motor applying an assist torque to a steering system;
a vehicle speed detecting section detecting a vehicle speed of the vehicle;
an engine rotational speed detecting section detecting an engine rotational speed; and
a motor control section for controlling drive of the electric motor based on an output from the vehicle speed detecting section, wherein the motor control section includes a failure determination section for determining failure of the vehicle speed detecting section on the basis of the vehicle speed detected by the vehicle speed detecting section and the engine rotational speed detected by the engine rotational speed detecting section; and
a racing detecting section detecting a racing state of the vehicle,
wherein the failure determination section determines that the vehicle speed detecting section malfunctions if the racing detecting section detects a non-racing state while the vehicle speed is zero and the engine rotational speed is equal to or greater than a predetermined rotational speed.
With such a constitution of the electric power steering apparatus, the failure determination section determines that the vehicle speed detecting section malfunctions, if the vehicle speed detecting section detects the vehicle speed of zero on condition that the engine rotational speed is equal to or greater than the predetermined rotational speed wherein the expected vehicle speed is greater than zero (viz. the vehicle would be actually moving) while the driver is not racing the engine. By this determination, since the racing is detected, it is possible to eliminate a determination error such that the vehicle speed detecting section is determined falsely as failure, even if the driver races the engine.
In this electric power steering apparatus, since the determination of failure of the vehicle speed detecting section concerns the vehicle speed, the engine rotational speed and the racing state as determination factors, it is possible to eliminate a determination error even if the driver races the engine. Therefore, the electric power steering apparatus ensures highly accurate determination of failure of the vehicle speed detecting section.
In the aforementioned electric power steering apparatus, the failure determination section may determine that the vehicle speed detecting section malfunctions if the racing detecting section detects a non-racing state for a determinative continuous-time and/or a first determinative integrated time while the vehicle speed is zero and the engine rotational speed is equal to or greater than a predetermined rotational speed.
With such a constitution of the electric power steering apparatus, the failure determination section determines that the vehicle speed detecting section malfunctions, if the vehicle speed detecting section detects the vehicle speed of zero on condition that an engine rotational speed is equal to or greater than the predetermined rotational speed wherein the expected vehicle speed is greater than zero (viz. the actual vehicle speed of the vehicle would no be not zero), and if such a condition continues for the determinative continuous-time and/or the first determinative integrated time while the driver is not racing the engine. By this determination, it is possible to eliminate a determination error such that the vehicle speed detecting section is determined falsely as failure, even in the case of abrupt starting. This is because the determination conditions consider the determinative continuous-time and/or the first determinative integrated time as sufficiently long time for which the vehicle speed detected by the vehicle speed detecting section after abrupt starting would be greater than zero.
In this electric power steering apparatus, since the determination of failure of the vehicle speed detecting section concerns the vehicle speed, the engine rotational speed and the racing state as determination factors, and further concerns the determinative continuous-time and/or the first determinative integrated time as determination conditions, it is possible to eliminate a determination error even in the case of abrupt starting. Therefore, the electric power steering apparatus ensures highly accurate determination of failure of the vehicle speed detecting section.
Further, in the aforementioned electric power steering apparatus, the racing detecting section may be incorporated in an engine control section, and the engine control section inputs a racing state signal to the motor control section.
With such a constitution of the electric power steering apparatus, the racing detecting section may be provided in the engine control section into which a signal of the racing state is inputted, and the racing state is determined by the racing state signal from the engine control section. Accordingly, the electric power steering apparatus determines the racing state with a simple constitution.
In this electric power steering apparatus, since the racing detecting section is incorporated in the engine control section, it is possible to simplify the construction and to thereby reduce the cost.
The wording xe2x80x9cvehicle speed is zeroxe2x80x9d indicates that the vehicle speed detected by the vehicle speed detecting section is zero. Therefore, even if the vehicle actually moves at an extremely low speed, as long as the vehicle speed detecting section detects the vehicle speed of zero due to the detection accuracy, the vehicle speed is regarded as zero. The wording xe2x80x9cshifting state is a vehicle driving statexe2x80x9d indicates that the shift range positions in a state where the vehicle is movable, and in the case of an manual transmission vehicle, the clutch pedal is not depressed and any one of transmission gears is set in, and in the case of an automatic transmission vehicle, a driving range such as a drive range, a low range or a reverse range is set in. Furthermore, the wording xe2x80x9cshifting state is not a vehicle driving statexe2x80x9d indicates that the shift range positions in a state where the vehicle is not movable, and in the case of an manual transmission vehicle, a neutral range is set in or the clutch pedal is depressed, and in the case of an automatic transmission vehicle, a neutral range or a parking range is set in. Furthermore, the wording xe2x80x9ca predetermined rotational speedxe2x80x9d indicates an engine rotational speed which inevitably makes the vehicle speed greater than zero (viz. the vehicle speed sensor inevitably detects the vehicle speed greater than zero) when the shifting state is a vehicle driving state, and the optimum value is set as a predetermined rotational speed in accordance with a kind of engine, idling engine rotational speed, etc. The wording xe2x80x9cdeterminative continuous-timexe2x80x9d indicates sufficient time, even in the case of abrupt starting, for the vehicle speed detecting section to detect the vehicle speed greater than zero after the engine rotational speed reaches the predetermined rotational speed. The determinative continuous-time is set as a continuous time. The wording xe2x80x9cfirst determinative integrated timexe2x80x9d indicates sufficient time, even in the case of abrupt starting, for the vehicle speed detecting section to detect the vehicle speed greater than zero after the engine rotational speed reaches the predetermined rotational speed. The first determinative integrated time is set as an integrated or accumulated time. Furthermore, the wording xe2x80x9csecond determinative integrated timexe2x80x9d indicates sufficiently long time wherein the driver usually would not race the engine for such a long time. The second determinative integrated time is set as an integrated or accumulated time.